It is known in the technical field of colour image processing to convert the red, green and blue (RGB) colour component signal samples of pixels representing an image into groups of component signal samples each having a luminance (Y) and two chrominance samples (U, V). Representing the RGB pixels as YUV signal samples provides a facility for reducing an amount of information, which must be communicated to represent a colour image. The reduction can be arranged by reducing or discarding some of the chrominance information without or with a reduced likelihood of causing a noticeable degradation to the reproduced image. This is because the human eye is less sensitive to loss of chrominance (colour) information from an image than luminance information.
The human eye's reduced sensitivity to loss of chrominance information can be used to reduce an amount of information, which is required to store a colour image. For example, it is known to reduce a number of samples required to store a digital colour image by converting pixels having RGB components into YUV form, discarding the UV chrominance values for every other pixel and storing the luminance value Y and storing the other chrominance values. The format of the resulting stored colour image is known as 4:2:2. When the colour image is reproduced, the UV chrominance values which have been discarded are reproduced from the UV chrominance values which have been stored.
For some applications, such as for hand held personal digital assistants or mobile radiotelephones having display devices, a reduction in an amount of information required to represent an image is particularly advantageous. Reducing the amount of information required to represent the image can provide an advantage, for example, with respect to the cost of the device as a result of a reduction in the size of a memory for storing the image. However, as far as possible, such a reduction in the amount of information required to represent an image should not affect the quality of the reproduced image.